The reference polymers and polymers with molecular imprints of carboxylic acids (MIPs-CA) — propionic (MlP-Propionic) and butyric (MIP-Butyric) acids — were synthesized on the surface of piezoelectric sensors using aromatic compounds by the non-covalent imprinting method. Molecularly imprinted polymer (MIP) is a polymer produced through molecular imprinting, which leaves cavities in the polymer matrix with affinity to a chosen "template" target molecule. The values of the imprinting factor and selectivity coefficients were calculated to assess the ability of MIPs-CA to recognize the target molecules. It is shown that the sensors modified by the molecularly imprinted polymers exhibit high selectivity for the acid that was a template during their synthesis. The detection limits for propionic and buty ric acids are 7.40 x 10~6 and 8.81 x 10-6 g/dm3, respectively. Correctness of the carboxylic acid determination in model solutions was verified in the spike/recovery tests. The relative standard deviation is less than 10%. The modified piezoelectric sensors were tested in analysis of the intermediate products of edible ethanol production (distillate of fermentation mixture, epyurat, bottom liquids of columns). The correctness of the determination of carboxylic acids in liquids was evaluated using an Agilent Technological 7890B GC Systems. The difference in the results of acid determination between both methods (piezoelectric sensor and chromatography-mass spectrometry) does not exceed 6%. The modified piezosensors expand the potential of rapid determination of carboxylic acids in the intermediate products of ethyl alcohol production.
In this article the molecularly imprinted polymers (MIPs) have been synthesized on the surface of piezosensors. The starting polymer for MIPs production was polyamic acid, which is a copolymer of 1,2,4,5-benzenetetracarboxylic acid and 4,4′-diaminodiphenyl ether. The caffeine served as the template. The quantum-chemical simulation was performed by the Gaussian 09 software using the DFT method at the B3LYP/6-31G(d,p) level with the basis set superposition error (BSSE) at the preliminary stage of the synthesis of the MIP for caffeine. The prepolymerization complexes were calculated to establish intermolecular interactions and obtain the optimum molar ratio between the template and polyamiс acid. It is shown that the constitutional repeating units of polyamic acid interact with the caffeine by forming H-bonds via carboxyl groups. The interaction energy first increases and then decreases with increasing the molar ratio of imprinting. Based on the quantum-chemical calculations, the optimal ratio of the reagents in prepolymerization mixture was set to 1 : 3 with the highest interaction energy (96.7 kJ/mol). Applying thermal imidization of solution of polyamic acid in the presence of a template, the molecularly imprinted polyimide has been synthesized by the non-covalent imprinting method. The ability of the obtained piezosensors to recognize the tempalte in model mixtures was experimentally evaluated. It was found that the range of detectable concentrations of caffeine is 3.1.10-6-10-1 mol/dm3 and the detection limit is 10-6 mol/dm3. Correctness of the caffeine determination in model solutions was verified in the spike/recovery tests. Piezosensors based on MIP were approved for the determination of the caffeine in tea varieties. It is shown that the concentration of caffeine in the aqueous solution increases with increasing brewing time. The relative standard deviation is less than 8%.
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